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diff --git a/web/xv6-intro.html b/web/xv6-intro.html deleted file mode 100644 index 3669866..0000000 --- a/web/xv6-intro.html +++ /dev/null @@ -1,163 +0,0 @@ -<title>Homework: intro to xv6</title> -<html> -<head> -</head> -<body> - -<h1>Homework: intro to xv6</h1> - -<p>This lecture is the introduction to xv6, our re-implementation of - Unix v6. Read the source code in the assigned files. You won't have - to understand the details yet; we will focus on how the first - user-level process comes into existence after the computer is turned - on. -<p> - -<b>Hand-In Procedure</b> -<p> -You are to turn in this homework during lecture. Please -write up your answers to the exercises below and hand them in to a -6.828 staff member at the beginning of lecture. -<p> - -<p><b>Assignment</b>: -<br> -Fetch and un-tar the xv6 source: - -<pre> -sh-3.00$ wget http://pdos.csail.mit.edu/6.828/2007/src/xv6-rev1.tar.gz -sh-3.00$ tar xzvf xv6-rev1.tar.gz -xv6/ -xv6/asm.h -xv6/bio.c -xv6/bootasm.S -xv6/bootmain.c -... -$ -</pre> - -Build xv6: -<pre> -$ cd xv6 -$ make -gcc -O -nostdinc -I. -c bootmain.c -gcc -nostdinc -I. -c bootasm.S -ld -N -e start -Ttext 0x7C00 -o bootblock.o bootasm.o bootmain.o -objdump -S bootblock.o > bootblock.asm -objcopy -S -O binary bootblock.o bootblock -... -$ -</pre> - -Find the address of the <code>main</code> function by -looking in <code>kernel.asm</code>: -<pre> -% grep main kernel.asm -... -00102454 <mpmain>: -mpmain(void) -001024d0 <main>: - 10250d: 79 f1 jns 102500 <main+0x30> - 1025f3: 76 6f jbe 102664 <main+0x194> - 102611: 74 2f je 102642 <main+0x172> -</pre> -In this case, the address is <code>001024d0</code>. -<p> - -Run the kernel inside Bochs, setting a breakpoint -at the beginning of <code>main</code> (i.e., the address -you just found). -<pre> -$ make bochs -if [ ! -e .bochsrc ]; then ln -s dot-bochsrc .bochsrc; fi -bochs -q -======================================================================== - Bochs x86 Emulator 2.2.6 - (6.828 distribution release 1) -======================================================================== -00000000000i[ ] reading configuration from .bochsrc -00000000000i[ ] installing x module as the Bochs GUI -00000000000i[ ] Warning: no rc file specified. -00000000000i[ ] using log file bochsout.txt -Next at t=0 -(0) [0xfffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b ; ea5be000f0 -(1) [0xfffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b ; ea5be000f0 -<bochs> -</pre> - -Look at the registers and the stack contents: - -<pre> -<bochs> info reg -... -<bochs> print-stack -... -<bochs> -</pre> - -Which part of the stack printout is actually the stack? -(Hint: not all of it.) Identify all the non-zero values -on the stack.<p> - -<b>Turn in:</b> the output of print-stack with -the valid part of the stack marked. Write a short (3-5 word) -comment next to each non-zero value explaining what it is. -<p> - -Now look at kernel.asm for the instructions in main that read: -<pre> - 10251e: 8b 15 00 78 10 00 mov 0x107800,%edx - 102524: 8d 04 92 lea (%edx,%edx,4),%eax - 102527: 8d 04 42 lea (%edx,%eax,2),%eax - 10252a: c1 e0 04 shl $0x4,%eax - 10252d: 01 d0 add %edx,%eax - 10252f: 8d 04 85 1c ad 10 00 lea 0x10ad1c(,%eax,4),%eax - 102536: 89 c4 mov %eax,%esp -</pre> -(The addresses and constants might be different on your system, -and the compiler might use <code>imul</code> instead of the <code>lea,lea,shl,add,lea</code> sequence. -Look for the move into <code>%esp</code>). -<p> - -Which lines in <code>main.c</code> do these instructions correspond to? -<p> - -Set a breakpoint at the first of those instructions -and let the program run until the breakpoint: -<pre> -<bochs> vb 0x8:0x10251e -<bochs> s -... -<bochs> c -(0) Breakpoint 2, 0x0010251e (0x0008:0x0010251e) -Next at t=1157430 -(0) [0x0010251e] 0008:0x0010251e (unk. ctxt): mov edx, dword ptr ds:0x107800 ; 8b1500781000 -(1) [0xfffffff0] f000:fff0 (unk. ctxt): jmp far f000:e05b ; ea5be000f0 -<bochs> -</pre> -(The first <code>s</code> command is necessary -to single-step past the breakpoint at main, otherwise <code>c</code> -will not make any progress.) -<p> - -Inspect the registers and stack again -(<code>info reg</code> and <code>print-stack</code>). -Then step past those seven instructions -(<code>s 7</code>) -and inspect them again. -Convince yourself that the stack has changed correctly. -<p> - -<b>Turn in:</b> answers to the following questions. -Look at the assembly for the call to -<code>lapic_init</code> that occurs after the -the stack switch. Where does the -<code>bcpu</code> argument come from? -What would have happened if <code>main</code> -stored <code>bcpu</code> -on the stack before those four assembly instructions? -Would the code still work? Why or why not? -<p> - -</body> -</html> |